Historically when blasting techniques are used to crack rock and concrete, an explosive charge is placed in a drilled hole followed by a stemming operation to help retain the force of detonation within the borehole. The stemming operation tends to involve packing the borehole above the explosive charge with some material, such as gravel, clay, and mud, to prevent the explosive force from simply being vented out of the borehole without cracking the rock. This operation is both time consuming and, in some instances, dangerous. Several stemming devices have been developed to eliminate this process; however, they have not seen widespread adoption given their cost, lack of effectiveness in stemming the blast hole or because they are bulky and difficult to use. Most of these known devices are placed in the borehole after the explosive charge.
Self-stemming devices which operate by blocking the borehole upon the action of the force released by the blast are also known. Such devices incorporate the blasting aspect, or charge, within or directly connected to the stemming aspect of the device. U.S. Pat. No. 137,196 issued to Gotham on Mar. 25, 1873 shows self-tamping torpedoes. The self-tamping torpedoes of Gotham were an improvement for blasting consisting of a plug, to which the cartridge is attached, having a diamond-shaped cone upon its top which fits between two sliding weights so that when the torpedo is exploded the plug spreads out thereby causing the blast to be exerted upon the adjacent walls of the hole. The device of Gotham, however, is a large device that is lowered on a cable into a pre-drilled borehole for large scale blasting. Furthermore, the device of Gotham does not have a single casing surrounding both the charge and the stemming aspect, and the casing it does have is a metal casing requiring a significant blast force to function.
Stemming devices and plugs that fit on the blasting cartridge, or have an opening to accommodate the blasting cartridge, are also known. U.S. Pat. No. 2,112,906 issued to Dietz on Jun. 5, 1935 shows a blasting plug which self expands upon detonation of an explosive thereby stemming the borehole, in which the explosive may be inserted into the base of the plug. Similarly, the blasting device of U.S. Pat. No. 1,616,048 issued to Holt on Jun. 30, 1925 operates by stemming a borehole as a result of the detonation of a charge located within the same structure as the self-stemming device. The blasting device of Holt, however, does not incorporate the charge and the stemming apparatus within a common casing, but incorporates the blasting device in a side opening of the stemming device. Likewise, U.S. Pat. No. 806,495 issued to Rasmussen on Dec. 5, 1905 discloses a means for plugging shot holes that operates by stemming the shot hole (borehole) as a result of the detonation of a charge located, at least partially, within the stemming device.
Devices with combined or attached blasting and stemming aspects are also known. U.S. Pat. No. 6,339,992 issued to Watson on Jan. 22, 2002 discloses a small charge blasting apparatus which includes a device for sealing pressurized fluids, including standard propellant, in holes. U.S. Pat. No. 4,546,703 issued to Thompson on Oct. 15, 1985 teaches a pre-packaged explosive charge, comprised of modules having a threaded male coupling end and a threaded female coupling end, which may also have a plug fitting threadably attachable to a charge module. U.S. Pat. No. 2,685,836 issued to Sauvage on Aug. 10, 1954 discloses a priming and tamping device for explosives in blast holes which can be attached to an explosive. U.S. Pat. No. 1,832,132 issued to Lanier et al. on Jan. 14, 1928 discloses a blasting shell which has a threaded part for stemming the shell in a borehole. The French patent FR 1,011,964 appears to show a blasting shell with a stemming aspect attached to one end thereof. German patents DE 651,287 and DE 305,020 also appear to show a blasting shell with a stemming aspect attached to one end thereof.
Various other known stemming devices and methods used to plug boreholes exist. U.S. Pat. No. 6,386,111 issued to Shann on May 14, 2002 discloses a stemming arrangement and method for blast holes which includes a hollow member, having a curved portion with stemming material contained therein, wherein the hollow member deforms upon detonation of an explosive thereby stemming the hole. U.S. Pat. Nos. 5,247,886 and 4,754,705, issued to Worsey, on Sep. 28, 1993 and Jul. 5, 1988 respectively, show mechanical stemming devices for use in boreholes which are placed outward from the explosive in the hole. U.S. Pat. No. 3,952,656 issued to Fox et al. on Apr. 27, 1976 discloses a stemming device which is composed of a resilient material capable of forming a seal along the walls of a borehole. U.S. Pat. No. 2,296,504 issued to Crater on Jul. 8, 1938 shows a “blasting plug” which consists of a two part stemming device that stems the borehole upon detonation of a charge disposed in the borehole adjacent the foot of the hole. U.S. Pat. No. 2,007,568 issued to Heitzman on Dec. 6, 1934 discloses a blasting plug (stemming device) which consists of two parts that stem the borehole upon detonation of a charge disposed inward from the blasting plug. The British patent, GB 2164, discloses a tamping method and devices which comprise a series of soft clay and hard clay plugs that operate together to stem a borehole.